Demonstrate external-window-mode in mus-demo

services/ui/ws/window_server.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "services/ui/ws/window_server.h"
 
 #include <set>
 #include <string>
 
 #include "base/logging.h"
@@ skipping 735 matching lines @@
 }
 
 void WindowServer::OnGpuChannelEstablished(
     scoped_refptr<gpu::GpuChannelHost> gpu_channel) {
   gpu_channel_ = std::move(gpu_channel);
   const std::set<Display*>& displays = display_manager()->displays();
   for (auto* display : displays)
     display->platform_display()->OnGpuChannelEstablished(gpu_channel_);
   // TODO(kylechar): When gpu channel is removed, this can instead happen
   // earlier, after GpuServiceProxy::OnInitialized().
-  delegate_->StartDisplayInit();
+  bool window_manager_connected = false;

[rjkroege, 2016/11/24 00:58:28]

I would have thought that GetFactories().size() > 0 would be sufficient and
safer against races at start? Probably sky@ knows for sure.

[Tom (Use chromium acct), 2016/11/28 20:47:37]

In my testing, there's an initial factory even when no window manager gets
connected.
sky@ can you verify this change?

+  for (auto* factory : window_manager_window_tree_factory_set_.GetFactories()) {
+    if (factory->window_tree()) {
+      window_manager_connected = true;
+      break;
+    }
+  }
+  delegate_->StartDisplayInit(window_manager_connected);
 }
 
 void WindowServer::OnSurfaceCreated(const cc::SurfaceId& surface_id,
                                     const gfx::Size& frame_size,
                                     float device_scale_factor) {
   WindowId window_id(
       WindowIdFromTransportId(surface_id.frame_sink_id().client_id()));
   mojom::CompositorFrameSinkType compositor_frame_sink_type(
       static_cast<mojom::CompositorFrameSinkType>(
           surface_id.frame_sink_id().sink_id()));
@@ skipping 40 matching lines @@
 void WindowServer::OnUserIdAdded(const UserId& id) {
   activity_monitor_map_[id] = base::MakeUnique<UserActivityMonitor>(nullptr);
 }
 
 void WindowServer::OnUserIdRemoved(const UserId& id) {
   activity_monitor_map_.erase(id);
 }
 
 }  // namespace ws
 }  // namespace ui